2/5 * 5/7 * 1/2 <== Group first pair of fractions to make
multiplication easier
(2/5 * 5/7) * 1/2 <== Multiply fractions in parentheses, keeping in
(10/35) mind all rules of fraction multiplication (i.e.
(2/7) cross-multiplying, etc.)
2/7 * 1/2 <== Multiply remaining fractions
1/7
The problem simplifies to 1/7.
Hope that helped =)